Technical Field
The invention relates to a process for extracting water from a liquid hydrocarbon and more particularly to a process for extracting water from a liquid hydrocarbon while solubilizing asphaltic precipitates in the liquid hydrocarbon.
Related Art
Crude oil produced at the wellhead under high pressure is flashed in a depressurization vessel. A vapor stream comprised of low molecular weight paraffinic hydrocarbon and water is taken off the top of the depressurization vessel. The vaporous hydrocarbon-water stream is condensed by compression and cooling. A solution of glycol and water is added to the resulting liquid hydrocarbon-water stream to extract the water therefrom. The composition is fed to a gravity separator where a water-free liquid hydrocarbon stream is taken off the top and a water-enriched glycol-water stream is taken off the bottom. The glycol-water stream is processed to remove a portion of the water and the remainder of the stream is recycled to the liquid hydrocarbon-water stream for continued use as a water extractant.
Substantial quantities of asphaltic precipitates are entrained in the hydrocarbon-water stream in the vapor state coming off the depressurization vessel. The asphaltic precipitates drop out of the hydrocarbon-water stream when it is condensed and contacted with the glycol-water stream since the asphaltic precipitates are insoluble in both the hydrocarbon-water and the glycol-water streams. The asphaltic precipitates accumulate continuously in the separator at the interface between the hydrocarbon and glycol-water phases. Eventually, the accumulated asphaltic precipitates must be removed by mechanical means which requires periodic plant shutdown.
A need exists for a process of extracting water from the low molecular weight paraffinic hydrocarbons without accumulating asphaltic precipitates in the process equipment. A number of asphaltene solvents are known in the art for dissolving asphaltenes accumulating in oil production wells and related equipment. U.S. Pat. Nos. 3,830,737 to Friedman et al; 3,914,132 to Sutton; 3,948,324 to Lybarger; 3,970,148 to Jones et al; 4,207,193 to Ford et al; 4,414,035 to Newberry et al; and 4,454,918 to Richardson et al all disclose the use of hydrocarbon-type solvents to dissolve asphaltenes in and around oil wells. However, none of the above-cited references relate to preventing the accumulation of asphaltic precipitates in an above-ground process for extracting water from low molecular weight paraffinic hydrocarbons. Such a process makes specific demands on an asphaltic precipitate solvent which are not encountered during production of oil. Particularly the combined presence of a glycol-water stream and a hydrocarbon-water stream creates a need for an asphaltic precipitate solvent which performs compatibly with all the components of the streams.